When Do I tell?

How old are you? 

Why wouldn't they approve? Because you're mooching off of them but spending mucho dinero on tri stuff? Or because they don't like being witness to your lifestyle?

Sounds to me like it is all over but the crying anyway.

If you tell them now, what are they going to do, put you on the curb?

If you don't tell them and go into total rebellion mode, it could be fun 

Seriously, honesty will set you free brother. It may not make them feel any better but it sure will make you feel a whole lot better.

... and to others... 

I would refrain from commenting here.   But I can't help but laugh...really, I thought this thread would be about coming out to one's parents as LGBT (I'm bi so I've actually had to do this about 15 years ago) not as an Ironman wannabe.   It's very funny, really.  

I think you have to face your fear and tell them NOW.  Don't go on trying to pump up this dream without their support.  They're already supporting you even if you do pay rent, and they know it as well as you do.  I think that's where your hesitation is coming from.

I wouldn't have to tell my parents I wanted to train for an IM or in any way seek their approval for it; I'd just do it.   That's a luxury/freedom that living on your own gives. 

So what you're saying is that you're parents will be mad because you won't be around on Saturdays and Sundays?

Here's the deal: If you all get along with you living at home and you are able to make good of the situation (i.e., save much more money than you would be saving by having a mortgage or rent; or not getting yourself into debt if debt's impossible to avoid by not living at home), then it should be all good. I don't see how Ironman should factor into the equation.

Just tell them. Who knows...maybe if you talk to them more and involve them more in your tri life, they might be more supportive .

just curious- what is your master's in?

and since you asked... I guess I am stunned that your  very first priority is not getting out on your own, that you would rather focus on IM,  buying a new bike etc.  You could still do tris on an older bike, and you could easily train for short distances while working an extra job in order to make the $$ needed to be a real grown up, ie, making your own decisions about what to tell mommy and daddy, and why their approval about your hobby matters-- among other things. Just sayin.

I cannot believe I just replied to this thread. 

and exactly why is the above in sarc format? 
Yeah, that's kinda what I was wondering...  being a edjucater and all...

what's a dangling preposition?  do you mean ending a sentence with a preposition?  That is only a rub when the same thing can be said without using the prep: "Where is she at?"  vs the correct "Where is she?" But "put up with" is OK.

Dangliing PARTICIPLES, on the other mano....